The present invention relates generally to lamp ballasts and, more particularly, to a ballast for a compact fluorescent lamp (CFL).
Conventional CFL ballasts employ an uncontrolled rectifier and an electrolytic storage capacitor for providing a stable dc bus for operating a high frequency oscillator. The oscillator provides a high-frequency, nearly sinusoidal current to the lamp. High-frequency operation results in higher lamp efficacy, and high-frequency electronic ballasts are typically smaller and lighter than typical line-frequency ballasts. Disadvantageously, the electrolytic capacitor is one of the most expensive and least reliable components of the lamp ballast; and without power factor correction circuits, the electrolytic capacitor may cause a highly distorted input ballast current. Removing the electrolytic storage capacitor from a conventional high-frequency electronic ballast will result in a circuit that must be restarted after each zero-crossing of the line voltage. The restart must occur at a sufficiently low voltage such that the lamp is driven for the majority of each line cycle. If the restart is slow, such as the restart provided by conventional start-up circuits, the lamp will remain off for a large portion of each line cycle, and flickering and reduced light output will result.
Therefore, it is desirable to provide an electronic CFL ballast which provides high efficacy and flicker-free operation, but does not require an electrolytic storage capacitor or power factor correction circuitry.